Reduced glutathione (γ-L-glutamyl-L-cysteinyl-L-glycine) is a reducing compound widely existing in organisms and is known to have a detoxification effect in the liver. Therefore, reduced glutathione has been widely used as a product such as a pharmaceutical product, a health food, and a cosmetic product, or a raw material or an intermediate thereof. A crystal of reduced glutathione is known to have two types of polymorphisms: α crystal and β crystal (Non-Patent Document 1) and, a crystal which is generally utilized as a product is the α crystal because of its physical properties.
However, the α-type crystal of reduced glutathione is likely to become a needle-like or elongated columnar crystal because the crystal growth in directions other than the long-axis (longitudinal) direction is slow. The ratio of the crystal length to the crystal width becomes large because of this property, and as a result, there arises a problem that the specific volume is increased and the powder flowability is deteriorated. In order to improve the powder properties, it is necessary to allow the crystal to grow not only in the longitudinal direction, but also in the lateral direction and the height direction.
Patent Document 1 describes the improvement of the powder properties of reduced glutathione and discloses a method in which a crystal of reduced glutathione is added as a seed crystal to an aqueous solution in which reduced glutathione is dissolved, followed by stirring, thereby precipitating reduced glutathione in the aqueous solution.